Thursday, October 28, 2010

Accuracy-->how reproducible a measurement is compared to other similar measurements
-->can be described as the correctness of a measurement

Precision-->how close the measurement (or average measurement) comes to the accepted or real value
-->can be described as the exactness of a measurement

*no measurement is exact
-every measurement is only one's best estimate, as it has some degree of uncertainty
-measurements are only exact when they are counted
eg. a family of 4

Absolute Uncertainty

-Uncertainty is expressed in the unit of measurement, not as a ratio or fraction
-there are 2 methods:Method 1:
1. Make at least 3 measurements
2. Calculate the average between the measurements
3.Calculate the different between the average and the lowest or highest reasonal measurement. The largest difference will be the absolute uncertainty.

Method 2:
1. Make the best precise measurement, estimate to a fraction 0.1 if the smallest segment on the instrument scale.

Relative Uncertainty and Sig. Figs.

Relative Uncertainty=Absolute uncertainty/estimated measurement

-relative uncertainty can be expressed as a percent, or with sig. figs.

Practice reading scales, and identifying the uncertainty of each measurement using method 2.

Inexact numbers - Ex. the length of the table is 124.34 mm then it is an inexact number.

Rounding numbers - round answers to the approximate - Example: if the number is over 5 then round it to a high number and if it is under five keep it that number. If the number equals to five the put a five

Wednesday, October 20, 2010

Rf value: the ratio of the distance traveled by the solute to the distance traveled by the solvent

Formula: Rf=d1/d2

D1 = distance traveled by solute

D2 = distance traveled by solvent

*Rf values vary from 0 to 1capillary action: in this case: when water is moving up the paper

solute front: (in this experiment) food colouring

solvent front: (in this experiment) water

Lab procedure:

Part 1: Setting Up

3 large testubes & 3 Erlenmeyer flasks. Label A, B, C

22cm chromatography paper

Use pencil to draw a line across strips 4cm from one end

Trim the end of the strip

Place 2cm deep water into each test tube

Part 2: Rf values of individual food colourings

Use a glass stirring rod to spot the strip with the colour

Write the colour at the top of the strip

Insert strip in test tube A

Observe the sample spot as the water goes up

Observe solute front and solvent front

Remove strip from the test tube. Immediately draw a pencil line across the top edge of the solvent front

Measure d1 and d2 calculate Rf for sample and record

Part 3: Separation of Mixtures onto Their Components

2nd strip with green colour, 3rd strip with unknown LABEL!

Insert strip in test tube B&C (see procedure in Part 2)

Record data on table 3!

Further Information:

The substances (solutes) to be analysed must dissolve in the solvent, which is called the mobile phase because it moves. The paper or thin layer of material on which the separation takes place is called the stationary or immobile phase because it doesn't move.

-centrifuge rapidly spins a test tube & separates substances of different densities, forcing the denser materials to the bottom

-works best with small quantities

Solvent extraction

-a component moves to a solvent shaken with a mixture

-works best with solvents that dissolve only one component

-mechanical mixture (2 solids): only one solid dissolves in the liquid & the desired solid is left behind

-solution: the solvent is insoluble because it is already present. It dissolves at least 2 substances & the unwanted substances remain

-if shaken in the separatory funnel, the liquids from layers

Distillation

-for a solution of 2 liquids

-heating the mixture triggers the low-boiling components to volatize (vapourize)

-evaporated components collect & condense

-the liquid with the lowest boiling point boils first, the vapour ascends to distillation flask & enters condenser, gas cools to a liquid, & distillate (condensed liquid formed from boiling) is dropped as a purified liquid

Chromatography

-a mixture is passed over a material that absorb some components more than others

Friday, October 15, 2010

-ACID: a covalent (non-metal + non-metal) bond formed from a negatively charged ion & a hydrogen ion dissolved in water
-when dissolved in water, ions separate
-chemical formula for an acid starts with a H (hydrogen)

-SIMPLE ACIDS
1) prefix: "hydro"
2) the last syllabe of the non-metal is replaced with the suffix "ic"
3) add the word "acid" at the end

Thursday, October 7, 2010

In the experiment, liquid dodecanoic acid (C12H34O2) was cooled in cold tap water until it reached a temperature of 25 degrees Celsius, and observations and temperature readings were taken every 30 seconds. The same process was used for the heating process, except the solid dodecanoic acid was placed in 55 degrees Celsius water. The purpose of the lab was to find the melting and freezing point of this substance (40 degrees Celsius) by graphing the results and finding the intersection between the heating and cooling processes. It was also discovered that melting point and freezing point are the same and interchangeable terms.

Monday, October 4, 2010

Science requires increasingly precise observations and detailed inferences. Observation takes too much time that science must be separated into different specialization. Individuals study matter in chemistry. One way to get a better understanding about matter is that you can carefully observe familiar substances, classify and generalize them on regular bases.

We learnt that few of the ways to identify matter is by their colour and taste. The characteristics of matter can also be recognized by the temperature at which matter changes from a liquid to a gas (boiling point) A mixture is twp or more kinds of matter that have separate identities. (impure) The idea of mixture and pure substance are used to describe matter.

Scatter light will appear if one shines a strong light on impure water and solutions Adding alum and lime to the water, then remove suspended particles from water. The water will not appear to have scattered lights Solutions are mixtures that look uniform throughout and do not scatter light Solutions such as sugar and salt in water are to be separated into their component parts using distillation

New techniques are still being developed in order to meet the environmental problems concerning today’s society. Pure substances have constant boiling point

oEx. As pure methanol is heated, the temperature gradually rises to 65C & begins to boil.The temperature remains constant throughout boiling.However, a mixture of 25% methanol & 75% water boils at around 86C, but the temperature continues to rise as it boils.

Chemical & Physical Changes

·Chemical changes: produce a new kind of matter with different properties

oEx. When sugar is heated in a test tube, it bubbles & forms a black solid while a colourless liquid forms on the walls of the test tube.The black solid & colourless liquid is both formed from an irreversibleprocess of decomposition that forms new substances with new properties.

oEx. Melting, boiling, & freezing are types of physical changes because the substance has all the same properties after a change of state, and the process is reversible.

Compounds & Elements

·Element: pure substances that cannot be decomposed

oSmallest particle: atom

·Compound: chemically combined elements & can be decomposed

oSmallest particle: molecule

p.36-39 Macroscopic observations are observations from what an individual can see, feel or smell. Whereas melting point, boiling point, heat of fusion, temperature and mass are all called macroscopic properties. On the other hand, microscopic model is to explain the performance of matter. Matter is made up of atoms. Atoms are usually expressed as spheres because chemists use spheres to help them

understand the microscopic world. Elements only contain one kind of atom. If the particles in an element vibrate, temperature will increase, therefore, an element can exist as a solid, liquid, or gas. Particles made of more than one atom are called molecules. The more outsized the particle is, the higher the boiling point will be. Energy such as heat and electricity are used to break down compound

Compounds can be formed by molecules or ions. Chemists need to check their conductivity in order to determine rather the compound is ionic or molecular.

·temperature remains constant because the heat that id supplied to it is used to overcome the forces of attraction that holds the particles together

·constant temperature = melting point

·heat energy overcomes the intermolecular forces id named as the latent heat of fusion

C

·all has completely melted

·solid -> liquid

C-D

·liquid state

·more heat energy = temperature increase

·particles move faster because kinetic energy increases

D

·liquid starts to boil

·molecules have got enough energy to overcome the faces of attraction between the particles in the liquid

·some particles will start to move freely

·liquid -> gas

D-E

·liquid & gaseous states

·the temperature unchanged

·heat energy absorbed to overcome intermolecular forces between the particles of the liquid rather than increase the temperature

·boiling point

E

·all of the liquid has turned into gas

E-F

·gas particles continue to absorb more energy & more faster

Here’s a chart that explains the heating and cooling of water:

Figure 2

KINETIC ENERGY is the energy that molecules possess as a resulr of their motion there are 3 types of Kinetic energy which a molecule can possess1. rational energy: causes a molecule to rotate around one of its axes; bond lengths ans bond angles don't change2. vibrational energy: changes the bond lengths and/ or angles between atoms in a molecule3. tanslational energy: causes the molecule to travel in a straight line from place to place, but has no effect on bond lengths and angles

eg. MICROWAVE OVENS supply energy which causes the water molecules in food and liquids to vibrate. As molecules absorb energy ans bump into each other, the food "heats up".http://www.youtube.com/watch?v=s-KvoVzukHo